Process for making 5-cyanovaleric acid, adipic acid or dimethyl adipate

ABSTRACT

Disclosed in a process for making (1) a compound of the formula NC—CH 2 —CH 2 —CH 2 —CH 2 —CO 2 R′, wherein R′ is H or C 1  to C 12  alkyl, or (2) adipic acid or (3) dimethyl adipate, using as the substrate, 3-pentenenitrile, (2) 3-pentenoic acid or methyl 3-pentenoate, respectively, by contacting the substrate with carbon monoxide and a nucleophile in the presence of a Group VIII metal, a selected ligand, and an acid promoter. The nucleophile, which (a) an alcohol or water, or (b) water or (c) methanol, respectively, in the presence of a Group VIII metal, preferably palladium, a selected phosphine ligand, and an acid promoter.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a division of U.S. application Ser. No. 10/667,519filed May 14, 2002, now U.S. Pat. No. 7,078,555 issued Jul. 18, 2006;which in turn is a continuation of U.S. application Ser. No. 09/997,506filed Nov. 19, 2001, now abandoned.

FIELD OF THE INVENTION

The present invention relates to a process for the conversion of (1)3-pentenenitrile to 5-cyanovaleric acid or its corresponding esters, (2)3-pentenoic acid to adipic acid and (3) methyl 3-pentenoate to dimethyladipate.

BACKGROUND OF THE INVENTION

Two processes are known in the art for the preparation of caprolactamfrom butadiene. The first process involves the following steps: (1)stepwise addition of two equivalents of hydrogen cyanide to butadiene toproduce adiponitrile, (2) partial hydrogenation of adiponitrile to form6-aminocapronitrile, (3) separation of 6-aminocapronitrile from fullyhydrogenated hexamethylenediamine and unreacted adiponitrile, and (4)hydrolysis of 6-aminocapronitrile and cyclization of the hydrolysisproduct to produce caprolactam.

The second process involves the following steps: (1) carbonylation ofbutadiene to methyl 3-pentenoate, (2) hydroformylation of methyl3-pentenoate to methyl 5-formylvalerate, (3) reductive amination ofmethyl 5-formylvalerate to methyl 6-aminocaproate, and (4) cyclizationof methyl 6-aminocaproate to caprolactam.

It would be desirable to develop a process that produces fewerby-products than the above processes and involves fewer reaction steps.A process that satisfies these needs could be based on the carbonylationof 3-pentenenitrile to 5-cyanovaleric acid or its corresponding esters.The process to produce caprolactam would involve the steps of: (1)hydrocyanation of butadiene to 3-pentenenitrile, (2) carbonylation of3-pentenenitrile to 5-cyanovaleric acid or ester, and (3) hydrogenationand cyclization of 5-cyanovaleric acid or ester to caprolactam.

In order to develop a successful process, an active, selective catalystthat operates under mild conditions for the carbonylation of3-pentenenitrile is needed. Previous attempts to produce methyl5-cyanovalerate or 5-cyanovaleric acid from 3-pentenenitrile were basedon the use of a cobalt catalyst. U.S. Pat. No. 5,434,290 discloses theuse of a cobalt catalyst, an activating solvent comprising carbonicdiesters, carbamates or ureas and CO pressures between 210 to 270 bar toconvert 3-pentenenitrile to methyl 5-cyanovalerate. U.S. Pat. No.4,508,660 discloses a similar process, but using sulfones as thepreferred solvent and CO pressures between 14 to 35 MPa. The rates ofcarbonylation reported in this patent are quite low, the turnoverfrequency calculated for example 2 of U.S. Pat. No. 4,508,660 gives 1.52mol/mol-hour. A similar situation is described in U.S. Pat. No.4,933,483.

Palladium-based catalysts for the carbonylation of olefins and diolefinsare known in the art. U.S. Pat. No. 5,028,734 discloses a process forthe selective carbonylation of conjugated dienes in the presence of analcohol and a catalyst system comprising a halide-free palladium salt, abidentate phosphine ligand and a protonic acid with a pKa value greaterthan 3. PCT patent application WO 00/56695 discloses a process for thecarbonylation of conjugated dienes by reaction with CO and alcohol inthe presence of a catalyst system including a source of palladiumcations, a phosphorus-containing ligand of structure X¹—R—X² and asource of anions. The preferred ligands are based on a9-phosphabicyclononyl group for X¹ and X² and a simple bridge for R. PCTpatent application WO97/38964 describes the use of the same catalystsystem for the carbonylation of ethylenically unsaturated compounds.

PCT patent application WO 98/42717 describes a catalyst of the formulaR¹>P—R²—PR³R⁴ for the carbonylation of terminal and internal olefins.The R¹>P moiety is a substituted 2-phosphatricyclo[3.3.1.1{3,7}]decylgroup where one or more of the carbon atoms are replaced by heteroatoms,in particular oxygen. Comparisons are made between phosphines such as(Me₃C)P(CH₂)₃P(CMe₃) (DTBPP) and1,3-P,P′-di(2-phospha-1,3,5,7-tetramethyl-6,9,10-trioxatricyclo[3.3.11{3.7}]decylpropane (DPA3). Carbomethoxylation of an internal-C14 olefin feed with apalladium-based catalyst using DPA3 as a ligand gives linear methylester with 78% selectivity at an average rate of 120 mol/mol-hour. Incontrast, using DTBPP as ligand under indentical conditions gives onlyan average rate of 5 mol/mol-hour.

PCT patent application WO96/19434 and Chem Comm., 1999, 20, 1877-1878describe the use of bidentate phosphines such as (di-t-butylphosphino)-o-xylene for the carbonylation of ethylene tomethylpropanoate. The patent application describes catalysts using thesebidentate phosphines as being unable to carbonylate propene. One skilledin the art might reason that if such catalysts are able to carbonylateethylene, but fail to carbonylate propene at any appreciable rate, thenthese same catalysts would be inactive for the carbonylation of internalolefins. Surprisingly, these catalysts are able to convert an internalolefin, namely 3-pentenenitrile, to the corresponding linear carboxylicacid, namely 5-cyanovaleric acid (or its alkyl esters). Additionallythese catalysts are able to convert 3-pentenoic acid to adipic acid, andto convert methyl 3-pentenoate to dimethyl adipate.

SUMMARY OF THE INVENTION

The present invention is a process for producing

(1) a compound of the formula NC—CH₂—CH₂—CH₂—CH₂—CO₂R′, wherein R′ is Hor C₁ to C₁₂ alkyl, or

(2) adipic acid, or

(3) dimethyl adipate,

comprising: contacting a substrate selected from the group consisting of(A) (B) and (C)

wherein substrate (A) is 3-pentenenitrile,

wherein substrate (B) is 3-pentenoic acid, and

wherein substrate (C) is methyl 3-pentenoate,

with a nucleophile (a), (b), or (c), respectively,

wherein nucleophile (a) is alcohol or water,

wherein nucleophile (b) is water and

wherein nucleophile (c) is methanol,

and carbon monoxide, in the presence of a Group VIII metal;

a ligand of the formula

whereinX is a substituted or unsubstituted bridging group selected from thegroup consisting of a divalent aryl, a divalent alkylene group, and adivalent combination of alkylene and aromatic groups; and

wherein R¹, R⁴, R⁷, and R¹⁰, independently are H, or C₁ to C₁₂ alkyl;

provided that R², R³, R⁵, R⁶, R⁸, R⁹, R¹¹ and R¹² independently are C₁to C₁₂ alkyl or cycloalkyl,

wherein R² and R³; R⁵ and R⁶; R⁸ and R⁹; and R¹¹ and R¹² may be takentogether to form a cycloalkyl group; and

a promoter, said promoter comprising a strong acid having a pKa in waterof less than 1 and, when the nucleophile is water, at least onecarboxylic acid.

DETAILED DESCRIPTION OF THE INVENTION

Disclosed herein is a process for preparing important, commerciallyuseful compounds, each having various functionality. The catalyst, whichis the metal plus the ligand, involved in the process of the presentinvention are very active and selective for the carbonylation of3-pentenenitrile when compared with other prior art catalysts based onligands such as1,3-P,P′-di(2-phospha-1,3,5,7-tetramethyl-6,9,10-trioxatricyclo[3.3.11{3.7}]decylpropane and 1,2-P,P′bis(1,5-dimethyl, 9-phosphabicyclononyl)ethane. Theligands of the present invention are bidentate phosphines of the generalformula shown below.

wherein

X is a substituted or unsubstituted bridging group selected from thegroup consisting of a divalent aryl, a divalent alkylene group, and adivalent combination of alkylene and aromatic groups; and

wherein R¹, R⁴, R⁷, and R¹⁰, independently are H, or C₁ to C₁₂ alkyl;

provided that R², R³, R⁵, R⁶, R⁸, R⁹, R¹¹, and R¹², independently are C₁to C₁₂ alkyl or cycloalkyl,

wherein R² and R³; R⁵ and R⁶; R⁸ and R⁹; and R¹¹ and R¹² may be takentogether to form a cycloalkyl group.

Examples of suitable X groups include, but are not limited to, thefollowing:—(CH₂)n-1,2-cyclohexylo-C₆H₄—CHCH₃—CHCH₃ortho-CH₂—C₆H₄—

Examples of suitable specific ligands include Ligands 1-5, shown below,wherein (tBu=tert-butyl).

Suitable Group VIII metals include cobalt, nickel, palladium, rhodiumand platinum. Particularly preferred is palladium. The palladiumcatalyst used in the process of the invention may be provided in theform of a palladium complex of the specified bidentate phosphine. It mayalso be generated in situ by adding a source of palladium and a sourceof the bidentate phosphine to the reaction. Suitable sources ofpalladium include palladium carboxylates, such as palladium acetate,propionate, butyrate or benzoate and palladium salts of mineral acids.Further sources include palladium complexes such as palladiumacetylacetonate, tris(dibenzylideneacetonate) dipalladium.

Some examples of suitable nucleophiles are water and primary andsecondary alcohols, such as straight chain and branched lower alkanols.

Some examples of suitable specific promoters include strong acids (pKain water of less than 1), such as methanesulphonic acid, chlorosulphonicacid, benzene sulphonic acid, trifluoromethane sulphonic acid. When thenucleophile is water, and the substrate is 3-pentenenitrile, the strongacid must be combined with at least one carboxylic acid, such as aceticacid, propionic acid, benzoic acid, o-toluoic acid, m-toluoic acid, orp-toluoic acid. The addition of at least one carboxylic acid can be usedwith methyl-3-pentenoate, but it is not necessary for the process toachieve the conversion.

The process may be carried out at a temperature in the range of about 80degrees C. to about 150 degrees C. and a carbon monoxide partialpressure in the range of about 200 to about 2000 psi.

Suitable solvents are one or more aprotic solvents such as ethers, e.g.diethyl ether, diethylene glycol dimethyl ether, anisole; aromaticcompounds, e.g. benzene, toluene, o-xylene, m-xylene, p-xylene; alkanes,e.g. hexane, heptane; nitriles, e.g. acetonitrile, benzonitrile,adiponitrile; and esters, e.g. methyl benzoate, ethyl acetate. Thereaction also can be carried out using the substrates and alcohol and/orwater as the solvent.

The molar ratio of the substrate and the alcohol or water can varywidely in the range of 1:1 to about 1:50, preferably between 1:1 toabout 1:10. The molar ratio of the substrate to the Group VIII metal canvary widely in the range about 10:1 to about 10000:1, preferably in therange of about 100:1 to about 2000:1. The molar ratio of the ligand tothe Group VIII metal can vary widely in the of range 1:1 to about 50:1,preferably in the range of 1:1 to about 5:1. The molar ratio of thestrong acid to the Group VIII metal can vary widely in the range 1:1 toabout 50:1, preferably in the range 1:1 to about 5:1. The molar ratio ofthe carboxylic acid to the Group VIII metal can vary between widely inthe range about 0:1 to about 10000:1, preferably in the range of about1:1 to about 2000:1.

Examples of suitable bidentate ligands are bis(di-t-butylphosphino)-o-xylene and bis(di-t-butyl phosphino) propane.Bis(di-t-butyl phosphino)-o-xylene has been described in J. Chem. Soc.,Chem. Comm, 1976, 365, and it is made by treating o-BrCH₂C₆H₄CH₂Br withHP(t-Bu)₂ and subsequent reaction with a base. Bis (di-t-butylphosphino) propane has been described in J. Chem. Soc., Dalton Trans.,1991, 863, and it is made by reacting 1,3-dibromopropane with LiP(t-Bu)₂in tetrahydrofuran as solvent.

The carbonylation process of the present invention can be performedbatchwise, semi-continuously or continuously. Preferably a continuousmanner of operation is used because it allows for higher molar ratios ofsubstrate to the Group VIII metal and lower residence times. Theproducts of the carbonylation of 3-pentenenitrile with methanol aremethyl 5-cyanovalerate, methyl 4-cyano-2-methyl butyrate, and methyl3-cyano-2-ethyl propionate. The products of the carbonylation of3-pentenoic acid with water include adipic acid, 2-methylglutaric acid,and 2-ethylsuccinic acid. The products of the carbonylation of methyl3-pentenoate with methanol include dimethyl adipate, methyl2-methylglutarate, and methyl 2-ethylsuccinate.

The invention is illustrated by the following non-limiting examples, inwhich the following terms are defined as indicated:

linearity: 100*[Moles of linear isomer]/[Sum of all isomers]

conversion: 100*[Substrate]/[Substrate]₀ where [Substrate]₀ is theinitial concentration of substrate

selectivity: 100*[Moles of linear product]/[Sum of all products detectedby GC analysis]

TOF (turnover frequency): [Moles of linear product]/[Moles ofpalladium][hour]

EXAMPLES Example 1 Synthesis of Ligand 1

Di-t-butyl phosphine (5.0 g, 0.0342 mol) was added dropwise to asolution of α,α′-dibromo-o-xylene (4.51 g, 0.0171 mol) in 50 ml acetoneand left to stir for 36 hours at ambient temperature in a nitrogendrybox. After removing the acetone under vacuum, the resulting whitesolid was rinsed with ether. Under nitrogen, a solution of sodiumacetate (12 g) in water (30 ml) was added to a suspension of the drywhite solid in ether (150 ml). The product was extracted under nitrogenwith ether (2×150 ml) and dried over NaSO₄. The combined ether layerswere vacuum-stripped to yield 1.5 g of yellow solid (22% yield). ³¹P NMR(C₆D₆): 25.1 ppm.

Example 2 Synthesis of Ligand 2

Lithium di-t-butylphosphine was prepared by reacting di-t-butylphosphine(5.0 g, 0.034 mol) with n-butyl lithium (21.0 ml, 0.034 mol) at ambienttemperature under nitrogen with stirring overnight. Four grams of thewhite solid were recovered by filtration (78% yield). 1,3 Dibromopropane(1.27 g, 0.00629 mol) was added dropwise to a solution of lithiumdi-t-butylphosphine (2.0 g, 0.0132 mol) in 50 ml THF and left to stir atambient temperature overnight. After completely removing the THF, thelithium salts were precipitated from the residue with minimal pentane.The salts were filtered out completely and the pentane was reduced toyield 1.5 g of colorless oil (69% yield). ³¹P NMR (C₆D₆): 27.3 ppm.

Example 3 Carbomethoxylation of 3-Pentenitrile with Ligand 1

A 100 ml Hastelloy B air motor stirred Parr (brand name) reactor wasloaded with a solution of the following composition: 25 g MeOH, 52 mgpalladium acetate, 32 g 3-pentenenitrile, 29 μl methanesulfonic acid,0.511 g o-dichlorobenzene and 0.135 g Ligand 1. After pressurizing thereactor to 500 psi of CO at the final temperature of 100° C., thereaction was monitored by GC during the five hour run. Results forlinearity, conversion, selectivity and turnover frequency (mol/mol h)are listed in Table 1. TABLE 1 Time [min] Linearity ConversionSelectivity TOF 0.00 98.50 38.05 59.88 15.00 98.38 54.97 65.25 2336.1530.00 98.31 63.88 67.88 1419.55 45.00 98.26 68.56 70.60 1064.50 60.0098.22 71.95 73.25 877.53 90.00 98.15 77.39 78.61 672.62 120.00 98.1081.85 83.28 567.61 180.00 98.03 89.63 90.18 447.07 240.00 97.99 94.7494.10 371.72 300.00 97.98 97.60 96.25 313.75

Example 4 Carbomethoxylation of 3-Pentenitrile with Ligand 2

Ligand 2 (0.122 g) was substituted for Ligand 1 in the procedureoutlined in Example 3. Results for linearity, conversion, selectivityand turnover frequency (mol/mol h) are listed in Table 2. TABLE 2 Time[min] Linearity Conversion Selectivity TOF 0.00 94.55 19.24 42.53 15.0093.87 30.58 52.42 323.20 30.00 93.69 47.50 57.70 282.29 45.00 93.6159.31 61.13 251.21 60.00 93.60 63.96 63.03 210.66 90.00 93.54 69.9166.51 162.56 120.00 93.58 72.70 68.92 132.14 180.00 93.52 78.28 73.58101.10 240.00 93.54 81.92 72.22 83.80

Comparative Example A

1,3-P,P′-di(2-phospha-1,3,5,7-tetramethyl-6,9,10-trioxatricyclo[3.3.1.1{3.7}]propane(0.149 g), prepared as described in Example 1 of PCT patent applicationWO 98/42717, was substituted for Ligand 1 in the procedure outlined inExample 3. Results for linearity, conversion selectivity and turnoverfrequency (mol/mol h) are listed in Table 3. TABLE 3 Time [min]Linearity Conversion Selectivity TOF 0.00 89.87 26.79 84.30 0.00 15.0089.85 37.11 85.71 641.43 30.00 89.78 43.72 86.72 385.20 45.00 89.7349.34 86.95 292.66 60.00 89.53 52.72 86.99 242.50 90.00 89.63 59.9487.38 182.93 120.00 89.71 63.98 87.53 145.51 180.00 89.72 68.22 87.78104.46 240.00 89.70 71.39 87.89 81.88 300.00 89.70 72.93 87.87 67.25

Example 5 Hydrocarboxylation of 3-Pentenitrile with Ligand 1

A 100 ml Hastelloy B air motor stirred Parr (brand name) reactor wasloaded with a solution of the following composition: 34 g diglyme, 54 mgpalladium acetate, 10 g 3-pentenenitrile, 46 mg methanesulfonic acid,0.5 g o-dichlorobenzene, 0.143 g Ligand 1, 5 ml degassed water and 10 gdegassed acetic acid. After pressurizing the reactor to 500 psi of CO atthe final temperature of 100° C., the reaction was monitored by GCduring the five hour run. Results for linearity, conversion, selectivityand turnover frequency (mol/mol h) are listed in Table 4. TABLE 4 Time[min] Linearity Conversion Selectivity TOF 15.00 98.57 11.74 53.56130.94 30.00 98.02 22.30 70.47 150.90 45.00 97.51 31.62 85.69 152.1060.00 97.43 36.21 88.49 131.10 90.00 99.32 48.45 94.73 121.99 120.0099.33 50.37 95.79 102.62 360.00 97.39 66.16 95.19 44.05

Comparative Example B

1,3-P,P′-di(2-phospha-1,3,5,7-tetramethyl-6,9,10-trioxatricyclo[3.3.1.1{3.7}]propane(0.149 g), prepared as described in Example 1 of PCT patent application98/42717, was substituted for Ligand 1 in the procedure outlined inExample 5. Results for linearity, conversion, selectivity and turnoverfrequency (mol/mol h) are listed in Table 5. TABLE 5 Time [min]Linearity Conversion Selectivity TOF 15.00 86.08 1.45 71.96 89.04 30.0086.34 4.75 77.06 68.09 45.00 86.64 5.48 78.72 57.18 60.00 86.91 8.2980.37 55.32 90.00 87.00 11.25 81.66 50.96 120.00 87.06 16.72 82.72 48.69180.00 87.23 22.54 84.08 43.81 240.00 87.16 28.02 84.51 37.77 300.0087.14 29.18 84.79 31.52 360.00 87.10 27.87 85.00 26.51

1. A process for producing adipic acid or dimethyl adipate, comprising:contacting a substrate selected from the group consisting of (B) and (C)wherein substrate (B) is 3-pentenoic acid, and wherein substrate (C) ismethyl 3-pentenoate, with a nucleophile or (c), respectively, whereinnucleophile (b) is water and wherein nucleophile (c) is methanol, andcarbon monoxide, in the presence of a Group VIII metal; a ligand havingthe formula

wherein X is a substituted or unsubstituted bridging group selected fromthe group consisting of a divalent aryl, a divalent alkylene group, anda divalent combination of alkylene and aromatic groups; and wherein R¹,R⁴, R⁷, and R¹⁰, independently are H, or C₁ to C₁₂ alkyl; provided thatR², R³, R⁵, R⁶, R⁸, R⁹, R¹¹, and R¹², independently are C₁ to C₁₂ alkylor cycloalkyl, wherein R² and R³; R⁵ and R⁶; R⁸ and R⁹; and R¹¹ and R¹²may be taken together to form a cycloalkyl group; and a promoter, saidpromoter comprising a strong acid having a pKa in water of less than 1and, when the nucleophile is water, at least one carboxylic acid.
 2. Theprocess of claim 1 wherein the ligand is selected from the groupconsisting of the


3. The process of claim 1 wherein said Group VIII metal is palladium. 4.The process of claim 1 wherein said promoter is methanesulphonic acid.5. The process of claim 1 wherein at least one of R¹, R⁴, R⁷, and R¹⁰ isH, C₁, C₂, or C₆ to C₁₂ alkyl.
 6. The process of claim 1 wherein thesubstrate is (C).
 7. (canceled)
 8. (canceled)